Thin polished plates such as silicon wafers and the like are a very important part of modern technology. A wafer, for instance, may refer to a thin slice of semiconductor material used in the fabrication of integrated circuits and other devices. Other examples of thin polished plates/films may include magnetic disc substrates, gauge blocks and the like. While the technique described here refers mainly to wafers, it is to be understood that the technique also is applicable to other types of polished plates and films as well. The term wafer and the term thin polished plate and/or film may be used interchangeably in the present disclosure.
Generally, certain requirements may be established for the dielectric properties of the wafers. Ellipsometry is an optical technique for the investigation of the dielectric properties of the wafers. Upon the analysis of the change of polarization of light, which is reflected off a sample (e.g., a wafer surface), ellipsometry can yield information about the sample. Ellipsometry can probe the complex refractive index or dielectric function tensor, which gives access to fundamental physical parameters and is related to a variety of sample properties, including morphology, crystal quality, chemical composition, or electrical conductivity. Ellipsometry is commonly used to characterize film thickness for single layers or complex multilayer stacks ranging from a few angstroms or tenths of a nanometer to several micrometers.
Spectroscopic ellipsometry is a type of ellipsometry that employs a broad band light source, which covers a certain spectral range (e.g., in the infrared, visible or ultraviolet spectral region). By covering a spectral range, the complex refractive index or the dielectric function tensor in the corresponding spectral region can be obtained, which gives access to a large number of fundamental physical properties.
However, testing results indicate that measurements obtained by the existing ellipsometry tools are not stable under certain circumstances. Therein lies a need for a ellipsometry tool with improved measurement stability.